The subject of the invention is an electric resistance furnace for melting metals, for maintaining them in a melted condition, and for production of metal alloys applicable particular to non-ferrous metals. The furnace operates with direct heating of bath by means of resistance heating elements.
Electric resistance furnaces known have, heretofore as a rule, heating elements located in the vault, walls and in the bottom of the furnace chamber or, as said in the Polish Patent No. 81,320, they are provided with heating elements shaped as one or several partitions located preferably parallel to the electrodes situated either directly in the bottom, or in the bottom in the vicinity of the ceramic walls of the melting bath. The partitions are built preferably of a uniform plate of ceramic material. These partitions are mounted in the bottom of the melting bath but their upper part reaches above or below the level of the metal being melted so that the whole surface of the partition or partitions be in contact with the melted metal or with the metallic bath.
The present Patent includes also a description of a resistance furnace in which the heating elements are in contact with the electrodes in the bottom or in the walls of the melting tank of the furnace, but so that at least one surface of the heating element is in contact with the melted metal or with a metallic bath, or, most favorably, built so that the bottom of the melting tank has the shape of the plate covering the botttom under which electrodes are accommodated.
The drawback of furnaces with heating elements built into the vault or in the side walls is their violent oxidation of charge. This is particularly the case if metals such as eg. zinc or aluminium are being melted by an intensive heating of the surface of the bath due to radiation of these heating elements. Melting losses encountered as a result of oxidation of the bath make it difficult to heat these baths because the layer of dross, has poor thermal conductivity. On the other hand, heating from below causes, in effect accelerated wear of the bottom plate, leading to leaking of the melted metal into the ducts of the heating tubes.
The design acc. to the Polish Patent No. 81,320 renders possible the melting of metals, particularly non-ferrous ones, with a good coefficient of utilization of electric energy and a simultaneous prolongation of the service life of the melting tank. On the other hand, the replacement or repair of the heating element is combined with serious difficulties exerting a negative influence on the quantity, frequency, and shutdown time, thus limiting the capacity of the furnace. The repairs are particularly troublesome and may even be dangerous for the repair workmen in view of the large size of the heating element, the high temperature of the furnace, and the presence of harmful gases.